1. Field of the Invention
The present invention relates to a circuit substrate, and more specifically a circuit substrate which can be baked or fired at a low temperature.
2. Description of the Prior Art
One of the most common ceramic materials used for circuit substrates in the prior art is alumina, which has good insulating qualities for use with products such as circuit substrates.
However, alumina requires a high baking or firing temperature in the region of 1500.degree. C. to 1600.degree. C. and there is only a limited number of types of conducting pastes which can be used with alumina circuit substrates. For example, with a multilayer circuit substrate in which the conducting paste and substrate are sintered at the same time, it is necessary to use conducting pastes of such as tungsten and molybdenum which can adequately resist the firing temperatures used with alumina. However, the electrical resistivities of tungsten and molybdenum are large, that is at 5.2.times.10.sup.-6 ohm-cm and 5.5.times.10.sup.-6 ohm-cm respectively, which are three times the resistivity of silver at 1.6.times.10.sup.-6 ohm-cm. Accordingly, in order to get conducting circuits of the same conductivity, it is necessary to make the conductor width about three times as large, resulting in the drawback that high density wiring is not possible.
Attempts have been made to add a glass component to reduce the firing temperature, but there is the problem of migration with multilayered wiring, and practical application of such a material is not desirable.
In addition, a circuit substrate must be moisture resistant.
It is therefore desirable to develop a circuit substrate which can be baked or fired at low temperatures without a deterioration in the insulating characteristics, in order to eliminate such drawbacks and problems which exist in the conventional technology.